1. Field of the Invention
The present invention relates to lock out valves for remotely actuated fluid cylinders.
2. Prior Art
Various lock out type pilot operated valves which provide a lock out feature have been advanced in the prior art, but most of these are integrated into control valves, or otherwise bulky and difficult to use. For example, a type of control apparatus that prevents leakage from a remote hydraulic motor is shown in U.S. Pat. No. 3,308,844, and a differential pressure responsive device for comparing pressures and for providing a latch comparator is shown in U.S. Pat. No. 3,570,516.
Additionally, it has been known to use pilot operated check valves in fluid circuits to prevent bleeding of fluid from a remote hydraulic motor such as a cylinder under load and to permit retracting of the cylinder when pressure is applied to the return side of the cylinder.
U.S. Pat. No. 2,420,554 shows a bypass valve for use between a normal control valve and the fluid pressure motor as well.
A hydraulic control valve that is connected to provide a flow blockage from a remote cylinder is also shown in U.S. Pat. No. 3,643,696.
Another lock out is shown in U.S. Pat. No. 3,568,718.